Electrolytes:- Part 2 – Sodium (Na+), Blood and Serum
Sample for Sodium (Na+)
- This test is done on the serum of the patient.
- A random sample can be taken.
- Heparinized plasma and whole blood without sodium heparin may be used.
- Twenty-four hours urine sample may be collected without the addition of preservatives.
- Can store the serum or urine at 2° C to 4 °C.
- Other samples can be:
- Gastrointestinal fluids.
Precautions for the estimation of Sodium (Na+)
- Avoid hemolysis (Although it does not cause much difference in serum or plasma sodium values).
- Lipemic serum needs to be ultracentrifuged unless the direct-selective electrodes measure sodium.
Indications for Sodium (Na+)
- This is the routine workup of the patient.
- This is done to evaluate electrolytes and acid-base balance.
- To evaluate water intoxication, water balance, and dehydration.
- It is estimated to diagnose and treatment of dehydration and overhydration.
Pathophysiology of Sodium (Na+)
- Sodium is the major cation of the extracellular fluid. It has a major influence on plasma osmolality.
- It is adjusted by the anti-diuretic hormone (ADH) and thirst receptors to maintain the plasma volume and osmolality.
- Aldosterone causes tubular reabsorption of sodium.
- Changes in the serum sodium reflect changes in water balance rather than sodium balance.
- Sodium is a very important cation from a quantitative standpoint and because of its influence on electric neutrality.
- The average adult body contains 80 grams of sodium.
- 35 grams is present in the extracellular fluid.
- Daily, the average person takes 3 grams of sodium in salt forms like chloride, sulfate, or other salts.
- Also, excrete the same amount of 3 grams per day.
- Dietary need of sodium = 90 to 250 meq//day.
- The normal daily diet contains NaCl 8 to 15 grams which are completely absorbed in the gastrointestinal tract.
- Sodium is the most common cation of the blood by almost 90%.
Sodium and the role of kidneys:
- 100% of sodium is filtered through the glomerulus.
- 70 to 80% is reabsorbed in proximal tubules (water and chloride).
- 20 to 25% is reabsorbed in the loop of Henle (with water and chloride).
- Kidneys are the main regulator of sodium in the body, which excretes the excess.
- Distribution of the sodium (Na+):
- The sodium level is the reverse of Potassium that sodium is 140 meq/L extracellular and 5 meq/L intracellular.
Functions of the sodium (Na+):
- Sodium is a major component of extracellular osmolality. It is almost half the osmolality of the plasma.
- So Sodium’s main function is to maintain osmotic pressure and acid-base balance.
- Sodium also helps to transmit nerve impulses.
- Sodium work with potassium and calcium to maintain the neuromuscular irritability for the conduction of nerve impulses.
- Neuromuscular, Sodium helps in the acid-base balance through sodium bicarbonate and sodium phosphate.
- Sodium takes part in cellular chemical reactions and membrane transport.
- The body can maintain the sodium level very well except for a few pathological conditions.
- Maintenance of sodium level depends upon:
- Renal blood flow.
- Carbonic anhydrase activity.
- Other steroids hormones control through:
- Anterior pituitary gland.
- Renin enzyme secretion.
- Antidiuretic hormone ( ADH ).
- Vasopressin secretion.
- Sodium is a result of a balance between dietary intake and renal excretion.
- Aldosterone acts by:
- Stimulating the Kidney to conserve sodium.
- And Decrease renal loss.
- ADH controls:
- Reabsorption of water at distal tubules.
- .This will affect by the concentration or dilution of sodium.
- Physiologically Sodium and water are interlinked.
- Increased free body water = Sodium diluted, Na concentration decreases, Kidney conserves sodium and excrete water.
- Decreased free water = Serum sodium will rise, now the Kidney will conserve water. Na+ level became normal.
Active transport of sodium (Na+):
- This is found in most of the cells, especially muscles and nerves.
- The excitable tissue has a high Na+, K+, and ATPase concentration.
- With the help of the ATPase enzyme in the cell membrane, three molecules of Na+ go out while only two molecules of K+ go in.
- So inside is negatively charged.
Hyponatremia level and Signs/Symtoms :
- When the level is < 125 meq/L (<135 mmol/L).
- < 120 meq/L is severe hyponatremia.
- The patient will feel weak.
- When Level < 115 meq/L.
- The patient will have confusion and lethargy.
- May progress to stupor and coma.
- There is a decreased glomerular filtrate rate, as seen in congestive heart failure.
- This is seen in the case of:
- low salt intake.
- There is premenstrual retention of sodium and water.
- Adrenocortical hyperfunction.
- This is seen in the case of:
Hypernatremia level and Signs/Symtoms:
- >160 meq/L is the critical value for the patients.
- The patient will have dry mucous membranes.
- Agitation and restlessness.
- Mania and convulsion.
- There is increased excretion of sodium in the urine.
- It is seen in:
- Adrenal failure.
- Diuretic therapy.
- Salt losing nephritis.
- Physiologically increased intake of salt.
NORMAL Sodium (Na+)
|Premature cord blood||116 to 140|
|Premature 48 hours||128 to 148|
|Newborn cord blood||126 to 166|
|Full-term||133 to 146|
|Infants||139 to 146|
|Child||138 to 145|
|Adult||136 to 145|
|>90 years||132 to 146|
|Urine 24 hours||meq/day|
|6 to 10 years||41 to 115||20 to 69|
|10 to 14 years||63 to 177||48 to 168|
|Adult||40 to 220|
|Child and adult||10 to 40|
|Cystic fibrosis||70 to 190|
|Feces||<10 (7.8 ± 2)|
|Without stimulation||6.5 to 21.7|
|After stimulation||43 to 46|
|CSF||136 to 150|
|28 weeks||124 to `48|
|48 weeks||115 to 139|
- To convert into SI units x 1.0 = mmol/L
- Sodium = 136 to 145 meq /L
- Infants = 133 to 142 meq /L.
- Premature infants = 132 to 140 meq/L.
- Urine = 40 to 220 meq/day with an average sodium intake of around 8 to 15 grams per day.
- (varies with dietary intake).
- CSF = 136 to 150 meq/L.
- Feces = mean value is <10 meq/day.
Causes of Hypernatremia (Increased serum sodium):
- Insufficient water intake.
- Primary aldosteronism.
- Cushing’s syndrome.
- Diabetes insipidus.
- Excessive sodium in intravenous therapy.
- Excessive sweating.
- Extensive thermal burns.
- Loss from GI tract.
Hyponatremia (Decreased serum sodium):
- Deficient dietary intake.
- Decreased sodium in the I/V therapy.
- Chronic renal insufficiency.
- Aspiration of pleural or peritoneal fluids.
- Excessive water intake.
- Congestive heart failure.
- Pleural effusion.
- Ectopic secretion of ADH.
- Pyloric obstruction.
- Malabsorption syndrome.
- Diabetic acidosis.
- Nephrotic syndrome.
- Absolute loss of sodium from the body:
- Prolonged vomiting.
- Excessive sweating.
- Prolonged diarrhea.
Hyponatremia, when the patient is hypovolemic, may be seen in:
- Renal losses due to:
- medullary renal disease
- Addison’s disease
- External losses due to:
- Gastrointestinal losses
Pseudohyponatremia may be seen in:
- This condition is usually caused by an excess of lipids in the serum. Serum sodium ions are not dissolved in the lipids.
Sodium (Na+) level in blood and urine in various conditions:
|Various clinical conditions||Sodium (Na+) level in the blood||Sodium (Na+) level in urine|
|Starvation||Normal||Normal or Increased|
|Congestive heart failure||Normal or decreased||Decreased|
|Acute renal failure||Decreased||Decreased|
|Chronic renal failure||Decreased||Increased|
|Renal tubular acidosis||Decreased||Increased|
|Adrenal cortical insufficiency||Decreased||Increased|
|Diabetes inspidus||Normal or increased||Normal|
Critical value when the patient needs an immediate intervention:
- Na+ < 120 meq/L. The patient will have weaknesses and neurologic symptoms.
- Na+ > 160 meq/L. This may cause heart failure.
- Too rapid correction of hyponatremia can lead to central pontine myelin-lysis.
- The too-slow correction will lead to cerebral edema.
Note: Please see more details on Serum electrolytes.